LPI 101-500 - LPIC-1 Exam 101, Part 1 of 2, version 5.0

The correct answer is C, s/txt$/bak.txt/. This regular expression will turn the input stream into the desired output stream by using the s command, which is used to substitute or replace a pattern with another pattern. The syntax of the s command is:

s/pattern/replacement/

The pattern is the regular expression that matches the text to be replaced, and the replacement is the text that replaces the matched text. The / symbol is used as a delimiter to separate the pattern and the replacement, but other characters can be used as well.

The pattern in this regular expression is txt$, which means that it will match the string txt at the end of the line. The $ symbol is an anchor that matches the end of the line. The replacement in this regular expression is bak.txt, which means that it will replace the matched string with the string bak.txt.

Therefore, the command s/txt$/bak.txt/ will replace the string txt at the end of each line with the string bak.txt, resulting in the following output stream:

txt1.bak.txt atxt.bak.txt txtB.bak.txt

The other regular expressions are incorrect for the following reasons:

A, s/^.txt/.bak/: This regular expression will not work as expected, because it has several errors. First, the pattern in this regular expression is ^.txt, which means that it will match the string .txt at the beginning of the line. The ^ symbol is an anchor that matches the beginning of the line. However, none of the lines in the input stream start with .txt, so the pattern will not match anything. Second, the replacement in this regular expression is .bak, which means that it will replace the matched string with the string .bak. However, this will not produce the desired output, because it will not append the string .txt to the end of the line, but rather replace the existing string with .bak.

B, s/txt/bak.txt/: This regular expression will not work as expected, because it has several errors. First, the pattern in this regular expression is txt, which means that it will match the string txt anywhere in the line, not just at the end. This will cause unwanted replacements in the middle of the words, such as atxt and txtB. Second, the replacement in this regular expression is bak.txt, which means that it will replace the matched string with the string bak.txt. However, this will not produce the desired output, because it will not preserve the original string, but rather replace it with bak.txt.

D, s/txt$/.bak/: This regular expression will not work as expected, because it has several errors. First, the pattern in this regular expression is ^txt$, which means that it will match the string txt only if it is the entire line. The ^ and $ symbols are anchors that match the beginning and the end of the line, respectively. However, none of the lines in the input stream are exactly txt, so the pattern will not match anything. Second, the replacement in this regular expression is .bak^, which means that it will replace the matched string with the string .bak^. However, this will not produce the desired output, because it will not append the string .txt to the end of the line, but rather replace the existing string with .bak^, which is not a valid file name.

E, s/[.txt]/.bak$1/: This regular expression will not work as expected, because it has several errors. First, the pattern in this regular expression is [.txt], which means that it will match any one of the characters inside the brackets, which are ., t, and x. This will cause unwanted replacements of single characters, such as the dot in the file extension or the letter t in the word atxt. Second, the replacement in this regular expression is .bak$1, which means that it will replace the matched character with the string .bak followed by the first backreference. A backreference is a way to refer to a part of the pattern that was captured by parentheses. However, there are no parentheses in the pattern, so the backreference $1 is invalid and will not work. Third, the replacement in this regular expression will not produce the desired output, because it will not append the string .txt to the end of the line, but rather replace the existing character with .bak$1, which is not a valid file name.

 The action that ensures that a faulty kernel module is not loaded automatically when the system boots is adding a blacklist line including the name of the offending module to the file /etc/modprobe.d/blacklist.conf. This file contains a list of kernel modules that are prevented from loading by the modprobe command, which is used to load and unload modules from the running kernel. By adding a line like blacklist  to this file, the module will be ignored by modprobe unless it is explicitly specified as a parameter. This way, the module will not be loaded at boot time or by other modules that depend on it. The other options are either invalid or do not affect the automatic loading of the module. Using lsmod --remove --autoclean without specifying the name of a specific module will not work, because lsmod does not have such options and it is only used to display the currently loaded modules. Using modinfo –k followed by the name of the offending module will not work, because modinfo does not have a -k option and it is only used to display information about a module. Using modprobe –r followed by the name of the offending module will only remove the module from the running kernel, but it will not prevent it from loading again at the next boot. Deleting the kernel module’s directory from the file system and recompiling the kernel, including its modules, is a drastic and unnecessary measure that will not only remove the faulty module, but also all other modules in that directory, and it will require a lot of time and expertise to perform. References:

Linux Essentials - Linux Professional Institute Certification Programs1

Exam 101 Objectives - Linux Professional Institute2

Linux Kernel Module Management 101 - Linux.com1

Chapter 2. Managing kernel modules - Red Hat Customer Portal2

The properties of a Linux system that should be changed when a virtual machine is cloned are the D-Bus Machine ID and the SSH host keys. The D-Bus Machine ID is a unique identifier for the system that is used by the D-Bus message bus system to communicate between applications. The D-Bus Machine ID is stored in the /etc/machine-id or /var/lib/dbus/machine-id file and it is generated during the first boot of the system. If a virtual machine is cloned without changing the D-Bus Machine ID, it can cause conflicts and errors with the D-Bus services on the clone and the original system. To change the D-Bus Machine ID, the file containing it must be deleted or emptied and the system must be rebooted12. The SSH host keys are cryptographic keys that are used by the SSH protocol to authenticate the identity of the system and establish a secure connection. The SSH host keys are stored in the /etc/ssh directory and they are generated during the first boot of the system or the installation of the openssh-server package. If a virtual machine is cloned without changing the SSH host keys, it can compromise the security and integrity of the SSH connections, as the clone and the original system will have the same keys. To change the SSH host keys, the files containing them must be deleted and the ssh-keygen command must be run to generate new keys34.

The other options are false or irrelevant. The partitioning scheme and the file system are not properties of a Linux system that need to be changed when a virtual machine is cloned, as they do not affect the functionality or the identity of the system. The permissions of /root/ are also not properties of a Linux system that need to be changed when a virtual machine is cloned, as they do not affect the security or the communication of the system. References:

Linux Essentials - Linux Professional Institute Certification Programs1

Exam 101 Objectives - Linux Professional Institute2

How to Clone Virtual Machine in VirtualBox - UbuntuMint3

Chapter 4. Cloning Virtual Machines Red Hat Enterprise Linux 7 | Red …4

The command that is used to change options and positional parameters for a running Bash is set. The set command allows the user to modify the behavior of the shell by enabling or disabling various options, such as -x (trace mode), -e (exit on error), -u (treat unset variables as errors), and others. The set command can also be used to assign values to the positional parameters, which are the arguments passed to the shell or a shell script. The positional parameters are denoted by $1, $2, $3, and so on, up to $9. The special parameter 0referstothenameoftheshellortheshellscript.Thespecialparameter# refers to the number of positional parameters. The special parameter $@ refers to all the positional parameters as a list.

To change the positional parameters, the set command can be used with the – option, followed by the new arguments. For example, the following command will set the positional parameters to “a”, “b”, and “c”:

set – a b c

After this command, $1 will be “a”, $2 will be “b”, 3willbe"c",# will be 3, and $@ will be “a b c”. The – option signals the end of options and prevents any argument that starts with a - from being interpreted as an option. Alternatively, the set command can be used with the - option, followed by the new arguments. However, this will also disable the -x and -v options, if they were previously enabled. For example, the following command will set the positional parameters to “-a”, “-b”, and “-c”, and turn off the trace and verbose modes:

set - -a -b -c

The set command can also be used without any option or argument, in which case it will display the names and values of all shell variables and functions.

The other commands are not valid or relevant for changing options and positional parameters for a running Bash. The history command displays the history list of commands entered by the user. The bashconf command does not exist. The setsh command does not exist. The envsetup command does not exist.

The nice command is used to start a process with a modified scheduling priority. The scheduling priority is a value that determines how much CPU time a process will receive from the kernel. The lower the priority, the more CPU time a process will get. The priority is also known as the nice value, because a process with a high nice value is being nice to other processes by giving up CPU time. The nice value ranges from -20 to 19, with -20 being the highest priority and 19 being the lowest. By default, processes are started with a nice value of 0, which means normal priority.

The nice command takes an optional argument -n followed by a number, which specifies the increment or decrement of the nice value from the default value of 0. For example, the command:

nice -n 5 /usr/bin/prog

will start the /usr/bin/prog process with a nice value of 5, which means a lower priority than the default. Similarly, the command:

nice -n -5 /usr/bin/prog

will start the /usr/bin/prog process with a nice value of -5, which means a higher priority than the default. If the -n argument is omitted, the nice command will assume a default increment of 10. For example, the command:

nice /usr/bin/prog

will start the /usr/bin/prog process with a nice value of 10, which means a very low priority. Note that only the root user can start a process with a negative nice value, as this requires special privileges.

Therefore, the command:

nice -5 /usr/bin/prog

is equivalent to:

nice -n -5 /usr/bin/prog

and will start the /usr/bin/prog process with a nice value of -5, which means a higher priority than the default. This means that the correct answer is B. /usr/bin/prog is executed with a nice level of 5.